The present invention relates to a magnetic resonance imaging apparatus, a magnetic resonance receiving apparatus, and a magnetic resonance imaging method.
A method called a line scan has been disclosed in a patent document 1. FIG. 3 is a conceptual diagram for describing a line scan. In the line scan, the operation of 90°-exciting and 180°-exciting spins of two slices S1 and S2 intersecting each other respectively and thereby receiving a spin echo generated from an intersection IT thereof, and subjecting the received spin echo to one-dimensional inverse Fourier transformation to obtain line images at the intersection is repeated while the intersection IT is parallel-moved in a phase direction Dph or the like within an imaging space. By collecting those line images, a two-dimensional image of a subject as seen in a projection direction Dpr is constructed.
[Patent Document 1] Japanese Unexamined Patent Publication No. 2001-61810
In the patent document 1, one two-dimensional image is obtained by moving the intersection IT placed on one plane. In contrast, it is considered that one two-dimensional image is obtained by moving the intersection three-dimensionally. FIG. 5 is a conceptual diagram showing one example illustrative of scan positions and a scan sequence where an intersection is three-dimensionally moved to obtain a two-dimensional image.
In FIG. 5, the direction orthogonal to the sheet indicates the longitudinal direction of the intersection IT. Each of rhombuses in the figure shows a line L′ corresponding to each scan position of the intersection IT in the form of a sectional shape of the intersection IT. Numerals in the lines L′ show a scan sequence. There is a case where lines L′ for a specific scan sequence are designated below by marking the lines L′ with numbers indicative of a scan sequence as in the case of a line L′ 1 and the like.
In FIG. 5, lines L′ are set onto a matrix M′ of 4 rows and 14 columns. Described specifically, one line L′ is set in each column and a plurality of lines L′ smaller than the number of columns are set in each row. And line images based on the scans of the lines L′ are collected or gathered thereby to obtain a two-dimensional image IMG of a subject as viewed in a projection direction Dpr parallel to a column direction.
Moving the intersection IT three-dimensionally in this way makes it possible to lengthen a distant scan interval between the lines L′ and relax interaction between the lines L′ while resolution of the two-dimensional image IMG in the phase direction Dph is being maintained high, as compared with the case in which the intersection is moved at one plane (only one row). An image or three-dimensional image of the subject as seen in the direction other than the projection direction Dpr can also be obtained.
The specific layout of the lines L′ and their scan sequence are set in consideration of various circumstances such as relaxing of the interaction between the lines L′, uniformization of the interaction between the lines L′ over a region of interest of the subject, etc.
In FIG. 5, the lines L′ are disposed in such a manner that the line L′ at the next row is shifted by one column with respect to the line L′ at one row in the right direction as seen from the sheet. A scan is sequentially performed in the column direction (projection direction Dpr) every row. At each row, the scan sequence is set along the rules common between the respective rows.
Thus, the temporal scan interval from the line L′ at the first row to the line L′ at the second row, and the temporal scan interval from the line L′ at the second row to the line L′ at the third row are equal to each other. When, for example, the temporal scan interval is expressed in the form of a difference in scan order, the scan interval from a line L′ 1 to a line L′ 5 is 5−1=4, and the scan interval from the line L′ 5 to a line L′ 9 is 9−5=4. They are equal to each other.
When, however, attention is focused on a line L′ 12, the temporal scan interval (12−9=3) from the line L′ 9 to the line L′ 12 becomes shorter than the temporal scan interval (9−5=4) from the line L′ 5 to the line L′ 9.Therefore, a reduction in signal strength due to spin saturation at the line L′ 12 becomes greater than that at the line L′ 9. Lines L′ 13 and L′ 14 are also similar to above. Thus, line-like unevenness of luminance occurs at positions corresponding to the lines L′ 12, L′13 and L′ 14 of the two-dimensional image IMG.